Health officials fear they have discovered the first case of someone catching swine flu within the UK, it emerged last night, as the number of confirmed cases in this country reached eight.

The "probable" case of domestic transmission involves a man who was in close contact with Iain and Dawn Askham, the Scottish couple who became the first confirmed British cases after returning from their honeymoon in Cancún, Mexico, with the virus.

Tests on the man found low levels of influenza A virus, and the samples were flown to the Health Protection Agency's main laboratories at Colindale, in north London, for further testing to establish whether he has swine flu.

The case emerged as three more people were diagnosed as infected with swine flu in Britain yesterday, bringing the total number of cases to eight. The HPA's laboratories are investigating a further 230 possible cases.

The Askhams said last night that they believed they had caught the virus on the flight back to Britain. The couple, who left hospital yesterday six days after being admitted, told the Daily Record that five men sitting near them on the Cancún to Birmingham flight had been coughing and sneezing throughout the journey. Mr Askham, 27, an IT worker, said he told his wife: "I think we're going to be getting off this plane with the plague."

Last night it emerged that a US security aide who helped arrange Barack Obama's trip to Mexico was suffering from flu-like symptoms, while Canada recorded its first case of person-to-person transmission of the virus, in Nova Scotia.

The outbreak has caused 12 deaths in Mexico and health authorities last night revised official figures, confirming 300 swine flu cases among a total of 679 people tested so far.

There are now also two confirmed cases in Virginia, a man and a woman who had both travelled to Mexico. It is understood they are recovering well.

Dr Harry Burns, Scotland's chief medical officer, said the new British patient was "probably more likely than less likely" to have swine flu because of his contact with the couple and the fact that influenza A viruses are rare at this time of year. He is being treated at home with the antiviral drug Tamiflu.

Nicola Sturgeon, the Scottish health secretary, said: "The circumstances around this person give us cause for concern. And that's why he's being treated as probable. That would be the first case of onward transmission from one of the original Mexico cases."

The latest confirmed cases involve a woman in Newcastle upon Tyne and two people in London. All eight confirmed cases contracted the flu in Mexico and have shown relatively mild symptoms after treatment with antiviral drugs.

The sharp rise in suspected cases over the previous 24 hours - from 78 to 230 - may indicate the heightened state of public awareness and alarm, as much as a sign of the disease's rapid spread.

EU governments failed last night to agree on pooling medical resources to combat the flu, and rejected French calls for a blanket ban on air travel to Mexico. The emergency meeting in Luxembourg of health ministers from the 27 countries in the EU agreed to coordinate policies and efforts, but indicated this amounted merely to sharing information on monitoring the speed of the virus's spread.

The newly confirmed case in Newcastle is a woman, recently returned from Mexico, who shared a flat with two local students.

Newcastle University said it would not close its facilities as a precaution. "This [patient] is not a student or a member of staff," the university said in a circulated email. "Neither of the students [who share the flat] has so far displayed any flu-like symptoms.

"Both students have received the antiviral Tamiflu. They and the university have been advised by the HPA that there is no need for the students to isolate themselves from the community unless they show symptoms."

Health officials in Paignton, where a 12-year-old girl was confirmed as having swine flu, said yesterday that dozens of other people in the area had complained of symptoms.

The girl, who is said to be "improving" is a pupil at Paignton Community and Sports College in Devon. Yesterday the school was shut and 340 pupils and staff issued with Tamiflu.

Dr Sarah Harrison, public health consultant for Torbay Care Trust, said: "We are aware of people who have flu-like symptoms. A number of people in this area are being tested. The numbers are more like dozens than hundreds."

After releasing the latest tally, the HPA said: "At this stage close contacts who should be offered antivirals as a precaution are individuals who have been exposed to a probable or confirmed case within the previous seven days, for longer than one hour, and within a distance of one metre. All cases up to now have been associated with travel to Mexico."

Earlier in the day the government's chief medical officer, Professor Sir Liam Donaldson, said he believed the UK would see "many more cases" of swine flu as the virus spreads, but that most people would make a good recovery. He described himself as "concerned, but not alarmed" by the decision by the World Health Organisation to raise the global alert level to phase five.